Review of Digital Pneumatic Servo Systems for Independent Metering Control: Valve Flow, Nonlinear Modeling, and Control Strategies

Due to high compressibility, small viscosity, low damping and stiffness, nonlinear friction, and valve port flow, pneumatic servo control systems are powerful nonlinear time-varying systems, making it difficult to guarantee their control accuracy, stability accuracy, and robustness. Digital pneumatic servo systems for independent metering control have been proposed to overcome these problems. In this paper, methods for achieving sufficient valve flow, nonlinear factor modeling, state estimation and compensation, and compound robust control strategies for these systems are summarized. Nonlinear factors include friction, pipeline loss, and cushioning. Furthermore, future research into digital pneumatic servo control technology is discussed based on the summarized research work and achievements of relevant scholars in pneumatic servo nonlinear control technology. Compared with traditional proportional servo control, the digital pneumatic control that is the focus of this paper has the advantages of low cost, simple control, and energy-savings, and it is highly consistent with the needs of Industry 4.0.